- A warning is emitted in the case of multiple relationships that
ultimately will populate a foreign key column in conflict with
another, where the relationships are attempting to copy values
from different source columns.  This occurs in the case where
composite foreign keys with overlapping columns are mapped to
relationships that each refer to a different referenced column.
A new documentation section illustrates the example as well as how
to overcome the issue by specifying "foreign" columns specifically
on a per-relationship basis.
fixes #3230